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Last modified
7/28/2009 2:38:42 PM
Creation date
4/16/2008 11:10:26 AM
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Template:
Weather Modification
Title
Final Report on Utah Cloud Seeding Experimentation Using Propane During the 2003/04 Winter
Date
3/1/2005
State
UT
Weather Modification - Doc Type
Report
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<br />I <br /> <br />I <br /> <br />targeting. Consequently, while the tracer gas passed by the TAR as intended in 89% of the cases, <br />mistargeting occUlTed during the remaining 11 % (4/35). <br /> <br />I <br /> <br />Only 34% of the variance was explained by the linear regression equation fitted to the northern edge <br />data. Again, and as expected, there was a tendency for more southerly plume transport as the wind <br />direction veered. But the relationship is weak and the wind direction data do not provide an accurate <br />means of predicting which cases will fail to transport plumes at the TAR. <br /> <br />I <br /> <br />The early 1994 SF6 observations, made during a range of westerly flow storm conditions, demonstrate <br />that HAS-released plumes routinely were transported over the Wasatch Plateau where the TAR was later <br />located. Such plumes would target the instrumented TAR and nearby GTR target gauge in the large <br />majority of sampled cases. Documentation of routine targeting is important physical evidence in support <br />of the 2003/04 randomized seeding experiment. <br /> <br />I <br /> <br />I <br /> <br />During early 1994 plateau top winds were measured at the head of a major canyon 2.9 km southeast of <br />the TAR. These directions were also compared to the 35 sets ofSF6 plume edge measurements. There <br />was no significant association with either southern or northern edges. All plateau top wind directions <br />were between 230 to 280 deg with a median of 252 deg. No doubt the local terrain had significant <br />influence on the observed surface wind direction. Although the Wasatch Plateau is generally oriented <br />north-to-south, the orientation of the major canyon immediately upwind of the wind observation site <br />would be expected to provide flow somewhat south of due west. <br /> <br />I <br /> <br />I <br /> <br />As previously noted, two purposes for further analyses of the early 1994 data were to examine wind <br />directions associated with successful targeting and to test the assumption that the TAR is usually targeted <br />by HAS-released plumes. As just discussed, the latter has been accomplished, and will be further verified <br />by examination of 1994/95 and 1995/96 data sets. HAS wind directions in the range observed during <br />early 1994, between about 200 and 290 deg, will result in HAS-released plumes reaching the TAR and <br />GTR in the large majority of cases. But only 3 samples had wind directions exceeding 270 deg" and one <br />of these had the plume transported south of the TAR. As will be discussed below, several 2003/04 EUs <br />had HAS winds greater than 270 deg, mostly related to an icing instrument problem. The early 1994 <br />tracer gas observations provide minimal information on HAS winds with a northerly component. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />As an air mass crosses a barrier, its depth decreases on the windward side, causing horizontal divergence <br />and decreasing relative vorticity (Hess 1959). This causes anticyclonic curvature over the windward side <br />ofthe barrier, giving the winds an additional northerly (or less southerly) component as the air moves <br />over the western slope in the case of the Wasatch Plateau. On the other side of the barrier, the opposite <br />occurs, giving lee of the mountain cyclogenesis. Rauber et al. (1988) used a basic assumption to <br />program a seeding targeting model that has been quite successful. The assumption is that the barrier- <br />perpendicular component of mass flux must remain constant as the air mass crosses the barrier. This <br />would increase the westerly component in the case of the Wasatch Plateau. This notion is supported by <br />the TAR directions for the EU data set. These are more from the west with less spread than the HAS <br />directions. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />4c. Examination of 1994/95 and 1995/96 Observations <br /> <br />I <br /> <br />Many pulsed seeding experiments with AgI or propane were conducted during the winters of 1994/95 <br />and 1995/96 as discussed by Super and Holroyd (1997) and Holroyd and Super (1998). One hour <br />releases were used the first winter and 30 min releases the second, all from the HAS. Plateau top <br />instrumentation, including heated wind sensors and a 2D-C ice particle imaging probe, were operated at <br />the TAR. While AgI seeding experiments used 60 min or 30 min continuous releases, propane <br />experiments used about 3 min AgI "tags" released at the beginning and end of each propane release to <br />define the propane plume. An acoustical ice nucleus counter was used to detect AgI at the TAR. <br />Appendix 2 of Holroyd and Super (1998) listed the experiments and the times of plume passage by the <br /> <br />I <br /> <br />I <br /> <br />13 <br /> <br />I <br />I <br />
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